The present invention relates to an optical switching matrix as an intermediate element in an optical data transmission link of a WDM system, having a large number of channels for the variable input and/or output coupling of a large number of optical channels.
Because of the meteoric increase in data traffic in communications networks, network operators require increasingly higher transport capacities which, in the backbone sector, lie at multiples of the basic capacities of 2.5 Gb/s, 10 Gb/s and, in the future, even 40 Gb/s. Such a basic capacity corresponds to a specific optical channel (OCh) which, in turn, corresponds to a specific carrier frequency. In this case, the multiplexing of these optical channels on an optical fiber is increasingly carried out with the aid of the optical wavelength division multiplex technique (WDM). In addition to simple point-to-point connections, interlinked network structures and ring structures are also needed. For the connection of data systems, these network structures require optical channels to be coupled into and out of the optical data transmission links.
A completely symmetrical Nxc3x97N matrix requires an implementation expenditure proportional to N2. However, this expenditure can be reduced significantly if, instead of complete symmetry, only specific preferred combinations of optical signals have to be implemented in a switching matrix.
It is an object of the present invention, therefore, to find a flexible optical matrix which can be produced with existing basic modules for coupling a number of optical channels into and out of a WDM ring transmission network. Such devices, used in conjunction with a wavelength division multiplex system, are also referred to as optical add/drop multiplexer (OADM).
The present inventor has discovered that it is possible to build up a configurable switching matrix with the aid of existing Mxc3x97N matrices and a network of multiple switches and multiple splitters which, via suitable control software, can be configured flexibly and quickly from outside.
In addition, it has been shown that an OADM according to the present invention can also implement various backup switching methods, by which the reliability of the optical transport network in which the OADM according to the present invention is used can be increased substantially and simply in the event of fiber faults.
For backup switching of optical channels, various methods can be used. For example, for ring architectures, the methods of xe2x80x9cOptical Channel Dedicated Protection Ringxe2x80x9d (OCh DPRING) and xe2x80x9cOptical Channel Shared Protection Ringxe2x80x9d (OCh SPRING) can be used. The implementation of these backup switching methods can be carried out within the switching matrix according to the present invention, since here access is made to the individual optical channels.
In accordance with these inventive ideas, the present inventor firstly proposes a unidirectional optical switching matrix as an intermediate element in an optical data transmission link of a WDM system having a large number of channels to couple a large number of optical channels variably in and/or out, a first side (West side) with N input channels and a second side (East side) with N output channels being provided to be incorporated into the optical data transmission link and, in addition, a third side (feeder side) having a large number of channels that are coupled in and/or out being provided, an Mxc3x97N input matrix for the N input channels being provided on the first side, and an Mxc3x97N output matrix for the N output channels being provided on the second side, and the first and second sides being connected to each other and to the input and output channels of the third side by a variably switchable network (ADP module). The basic constituents of such a large switching matrix can be simple, commercially available optical Mxc3x97N matrices, optical switches and splitters, which are connected together in the manner according to the present invention.
In an embodiment, it is also proposed to design the optical switching matrix bidirectionally in that, additionally, an Mxc3x97N output matrix for an additional N output channels is provided on the first side, and an Mxc3x97N input matrix for an additional N input channels is provided on the second side.
In a preferred embodiment of the optical switching matrix according to the present invention, it is proposed that the variably switchable network have a distributor with a distributor input and at least two distributor outputs on at least one input channel, downstream of the Mxc3x97N input matrix of the first and/or second side, at least one distributor output leading to an output channel on the respectively opposite side, and at least one distributor output leading to an output on the third side.
In addition, the variably switchable network can have a controllable switch having at least two switch inputs and a switch output on at least one output channel upstream of the Mxc3x97N output matrix of the first and/or second side, at least one switch input leading to an input channel on the respectively opposite first or second side, and at least one switch input leading to an input channel on the third side.
In addition, the variably switchable network can have a distributor with a distributor input and at least two distributor outputs on the third side (feeder side) on at least one input channel, at least one distributor output leading to an output channel on the first or second side.
In a further embodiment, provision is also made for the variably switchable network to have a switch (feeder switch) with a switch output and at least two switch inputs on at least one output channel, at least one switch input leading to an input channel on the first or second side.
The part components provided in the optical switching matrix according to the present invention can be square matrices, that is to say Nxc3x97N matrices. Pursuant to this, for example by connecting together four Nxc3x97N matrices, a 4Nxc3x974N switching for an OADM may be set up, N switches and N distributors preferably being provided on the third side (feeder side).
In this case, the variable network can be constructed in such a way that a single-redundancy (1+1) channel backup circuit or a ring backup circuit with distributed redundancy (shared protection) results, as defined in existing standards, for example ITU-T G.841.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.